Rapid cold hardening in the predatory mite Euseius (Amblyseius) finlandicus (Acari: Phytoseiidae)

A rapid cold hardening response was studied in diapause and non-diapause females of the predatory mite Euseius finlandicus. When laboratory reared diapause and non-diapause females were transferred and maintained from the rearing temperature of 20 degreesC for 2 h to -11.5 degreesC and -10 degreesC, 10 to 20% survived respectively. However, conditioning of diapause females for 4 h at a range of temperatures from 0 to 10 degreesC before their exposure for 2 h to -11.5 degreesC, increased survival to approximately 90%. Similarly, conditioning of non-diapause females for 4 h at 5 degreesC before their exposure for 2 h to -10 degreesC increased survival to 90%. A similar rapid cold hardening response in both diapause and non-diapause females was also induced through gradual cooling of the mites, at a rate of approximately 0.4 degreesC per min. The rapid increase in cold tolerance after prior conditioning of the mites to low temperatures, was rapidly lost when they returned to a higher temperature of 20 degreesC. Rapid cold hardening extended the survival time of diapause and non-diapause females at sub-zero temperatures. The cost of rapid cold hardening in reproductive potential after diapause termination was negligible. In non-diapause females, however, the increase in cold tolerance gained through gradual cooling could not prevent cold shock injuries, as both fecundity and survival were reduced. (C) 2001 Elsevier Science Ltd. All rights reserved.